The present invention relates to an electric motor with a converter unit. Highly diverse types of motors are known from the related art. For example, standard asynchronous motors are the most common types of drives used in industry. These types of motors are inexpensive, very robust, and quiet-running. Asynchronous motors of this type have various disadvantages, however, such as a fixed speed and direction of rotation, and the fact that a separate start-up device is required. In addition, they are inefficient at partial loads, and the cos phi power factor is poor. In addition, active braking cannot be carried out with motors of this type.
To overcome these disadvantages, the trend in the related art has been to operate proven asynchronous motors with a converter that powers the motor. With the aid of this converter, basically all disadvantages may be eliminated. The trend is therefore increasing toward motors that are operated using converters.
The act of providing a converter has various disadvantages, too, such as additional costs, a greater amount of space required in the switch cabinet, the development of additional heat in the switch cabinet, and noise radiation resulting from the pulse-width modulation (PWM), and the resultant need for interference suppressor filters.
Ideally, when a converter is used, however, there is no need for (expensive) mains supply interface components, which are common with standard motors. For example, there is no need for a starting circuit-breaker or a tripping unit for temperature monitoring, or for a star/delta connection-type starter or a motor starter. Nor is there a need for a contactor combination for the pole-changing or the reversal, or for a mains contactor, when an operational voltage disconnection is not required (that is, when the converter includes an electronic starting lockout). A direct current braking device is not required, either.
Converters are therefore being used to an increasing extent in the related art, with the result that combinations of motors and converters (“converter motors”) are becoming more common. A known means for achieving the object is to use a converter, which is screwed onto the motor in place of a terminal box. The motor is an unmodified, standard motor, and the converter is a separate functional unit, which may also be installed next to the motor, as an option. This combination may be connected directly to the mains, since the mains filter is integrated in the converter.
A separation is carried out in this case, in particular a thermal separation between the motor and the converter. The reason for this is to ensure that emergency operation of the motor directly from the mains may be carried out if the converter fails. Motors are therefore typically wound for mains voltage (400V, 50 Hz). The advantages of locating the converter directly on the motor are that less space is required in the switch cabinet, and heat generation is prevented. In addition, there is no need to shield the motor cable.
The disadvantage of systems of this type is that the converter unit is often just as large as the motor itself. Given low nominal power in particular, the converter is often designed to be larger than the motor itself. The reasons for this are that the converter has its own cooling system, and that the converter is connected with the motor via an intermediate housing in which the terminals are located.
Basically, heat exchange between the converter and the motor housing is prevented in the known objects by utilizing thermal decoupling. A position pick-up for regulating rotational speed or position is basically not integrated, or doing so requires high additional costs.